The present invention relates to instruments for obtaining tissue samples to be used for example in biopsy procedures. More particularly, the invention relates to improved instruments for propelling needle assemblies to sample the diagnostic tissue.
In the effort to improve this diagnostic sampling, particularly of prostate tissue, needle assemblies have been developed which capture a longitudinal, or core sample of the tissue which is extracted for diagnosis. Conventionally, the needle assembly has a hollow outer cannula needle through which a cutting, stylet needle is slidably projected to cut and capture a core of the tissue within a notch formed in the inner stylet as described for example in U.S. Pat. No. 4,776,346. The sampling procedure for such a needle assembly requires separate motions of the inner stylet and the outer cannula to accomplish the tissue capture. The instrument described in the aforementioned patent allows a physician to manually perform the dual motions of the needle assembly, however, each motion requires a separate and different manual activation. The separate manual movements to activate the needle operation involve the potential for displacement of the intended needle alignment and motions, and the danger of puncturing organs adjacent to the intended tissue A similar instrument allowing simplified activation of the needle assembly movements is described in U.S. Pat. No. 4,699,154, however, the described instrument requires multiple propulsion springs and release mechanisms in order to produce the needle motions. These disadvantages are eliminated with the instruments in accordance with the present invention.